Posterior spinal laminectomies are performed to decompress the spinal cord and/or nerve roots contained within the spinal canal. Decompressive laminectomies are performed to relieve degenerative stenosis, herniated/bulging discs, and traumatic stenosis. In addition, they are performed in order to access the spinal canal to enable the removal and/or treatment of benign or malignant tumors, vascular lesions, abscesses, other masses, syrinxes, and a host of other conditions.
Posterior laminectomies can be performed on every spinal element throughout the entire spine including cervical, thoracic and lumbar. Laminectomies leave the posterior neural elements exposed without their native protection provided by dorsal protective lamina/spinous processes, and can lead to short and/or long term deformity and/or kyphosis. Delayed kyphosis, particularly in the cervical spine is typically remedied with the performance of posterior instrumented fusions which have an increased risk of neuro-vascular complications.
Kyphotic deformities secondary to laminectomies are more prevalent in the cervical spine. As a result of this multiple versions of a technique called laminoplasty have been developed for the cervical spine. This technique entails, opening up the lamina on one side, and using a variety of plates and screws to reattach the opened lamina to the remaining native lamina. These techniques can be cumbersome, time consuming, and also may have increased likelihood of dural tears, and nerve root injuries compared to the performance of straight forward laminectomies. However, laminoplasties as a result of protecting the cervical dura may have a less likely chance of leading to delayed kyphotic deformities.
Currently there is limited attention/technology developed for laminoplasty techniques related to thoracic/or lumbar spines. There are no other known devices that provide total artificial spinous process-laminar replacements (prostheses) mechanically designed for the explicit purposes of laminoplasty, i.e. to enlarge the diameter of the spinal canal and reconstruct the natural spinolaminar anatomy to protect exposed neural elements.
U.S. Application to Vittur et. al (Spinous process implants and methods; U.S. Pub No: US 2008/0281360 A1) describes embodiments of a replacement spinous process with a flat or concave single piece laminar portion extending anteriorly and inferiorly, and not laterally. It's lack of concavity when applied to the spine does not allow for the expansion of the dural spinal space, which is mandatory for a stenotic thecal sac decompression, and hence is not suitable for the purposes of a decompressive laminoplasty/laminectomy. Its primary purpose is to replace injured spinous processes, in order to “provide and maintain separation between spinous processes”. The device is predominantly contoured to fit an inter-spinous spacer (specifically the DIAM spinal stabilization system of Medtronic), to distract spinous processes. It is not attached directly to the lamina. It is somewhat cumbersome with laterally protruding separate or built-in connecting elements which in turn are attached to anchors which in turn are secured to pedicle screws. No embodiment is capable of replacing more than one spinal element.
Other device embodiments presented by Vittur et. al. (Posterior stabilization and spinous process systems and methods; U.S. Pub. No. US 2008/0281361 A1, Pub date Nov. 13, 2008) include multiple embodiments of spinous process replacements which do not in any way geometrically reproduce the spinous process anatomy, and are essentially devices designed to crosslink two elongated parallel bars, which in turn are attached to pedicle screws. This device “is integrated with posterior stabilization instrumentation so that interspinous stabilization procedures can be completed even if the spinous process of the patient is removed . . . ” This device is not designed, or considered, to be, a total spinolaminar replacement, nor is it suitable for a laminectomy/laminoplasty. It does not attach directly to the spine, rather it is attached to parallel bars, which in turn are secured by pedicle screws which are attached to the spine.
U.S. Applications and Patent to Bruneau et. al (Artificial Spinous Process for the Sacrum and Methods of its use; U.S. 2007/0191834 A1—Pub Aug. 16, 2007), U.S. Pat. No. 7,837,711 B2; patented Nov. 23, 2010, and U.S. 2010/0268277 A1; Pub Oct. 21, 2010) describe a device that attaches to the sacrum and provides a support for positioning an implant to dampen the relative movements during flexion and extension exclusively between the sacrum and the fifth lumbar vertebrae. The purpose of this implant is to fortify, not replace, the S1 (first sacral) vertebrae, which may not be well defined and therefore inadequate to support an implant. Specifically, the device is not a spinolaminar replacement or a spinous process replacement. It is positioned along the lateral sides of the S1 process, and its lateral extensions are uniquely designed only for the sacral anatomy. Another embodiment described by Bruneau et. al has extensions which then connect to anchors which are screwed into the sacrum. This device is not adaptable for any position of the spine other than L5-S1. Furthermore, is it not directly attached to the lamina, but rather has lateral protruding elements which in turn are attached to lateral extensions which in turn are attached to sacral screws. This device replaces neither lamina nor spinous processes.
U.S. Patent to Gielen et al. (Lamina Prosthesis for delivery of medical treatment; U.S. Pat. No. 6,481,440 B2; Nov. 19, 2002) disclose a unilateral laminar prosthetic which only replaces a portion of a lamina unilaterally and is configured with means for delivering a variety of medical treatments, such as electrodes, fluid channels, catheters and drugs. It is not secured to remaining lamina; rather it is secured to vertebral bodies with conventional bonding glue or similar technology. This device substitutes a portion of a hemi-lamina for the explicit purposes of delivering ancillary treatment. It is not considered a total spinolaminar replacement, nor does its design reflect such a purpose.
U.S. Application to Williams (Bone anchored surgical mesh; Pub. No. US 2006/0264948 A1; Published Nov. 23, 2006) describes a bone anchored surgical mesh to cover the spinal cord after a laminectomy. This perforated mesh offers an inadequate protective cover of posterior spinal elements, and lacks the strength of a total spinolaminar replacement which recreates the solid anatomy of the spinal posterior elements which is necessary to protect and strengthen the post-laminectomy spine.
U.S. Application to Mir (Spinous Process cross-link; US 2010/0249842 A1; Pub: Sep. 30, 2010) presents a prosthetic spinous process crosslink similar to Vittur et al. which attaches to the spine by gripping feet extensions which grip rods which are secured to pedicle screws, or directly grip pedicle screws.